The Array multifocal lens--functional principle and clinical results

BACKGROUND: Common refractive bifocal IOLs feature 2 or 3 spherical zones with different refraction; the design of the Array multifocal IOL consists of 5 concentric zones, each of them providing a progressive near addition with multiple foci by means of an aspherical surface. METHODS: As a part of a prospective study, distance and near visual acuity, contrast sensitivity, glare and depth of field were examined in 15 patients with the Array lens and a monofocal control group 12 months after implantation. Subjective assessment of the optical quality was performed by detailed asking for optical symptoms. Results were retrospectively compared with the one year follow-up of 15 patients with diffractive bifocal IOLs. RESULTS: No difference was found for best corrected far and near visual acuity and sensitivity for high contrasts. Glare and sensitivity for low contrasts of the monofocal IOL was significantly superior to both multifocal models. Array IOL and diffractive IOL achieved a near acuity of Nieden 2-1 with only distance correction; defocus curves revealed an increase in the depth of field, but with a superiority of the Array lens in intermediate imaging. Optical symptoms as halos were much more frequent in patients with the diffractive IOL than in the Array group. CONCLUSIONS: Functional results of the Array multifocal IOL seem to be comparable to those of the diffractive bifocal IOL, but with the advantage of an improved intermediate imaging and a reduction of optical side effects.     

A prospective evaluation of a diffractive versus a refractive designed multifocal intraocular lens

OBJECTIVE: To evaluate prospectively a diffractive (811E, Pharmacia; power add +4.0 D) versus a refractive (PA154N, Allergan; power add +3.5 D) designed multifocal lens. PARTICIPANTS: Eighty patients planned for cataract surgery without additional ocular pathologies were randomized into the diffractive or refractive group, respectively. INTERVENTION: A standardized no-stitch phacoemulsification with implantation of one of the two multifocal lenses was performed in each patient. MAIN OUTCOME MEASURES: Distance and near-visual acuity, contrast sensitivity, low contrast visual acuity, glare visual acuity, and depth of focus were measured after surgery. RESULTS: All treated patients had best-corrected visual acuities of 20/30 or better. Near-uncorrected vision was significantly better (P < 0.0001) with the diffractive lens (mean, J1) than with the refractive lens (mean, J4). Low contrast visual acuity (61 +/- 12% versus 59 +/- 9%), glare visual acuity (39 +/- 19% versus 38 +/- 14%), and contrast sensitivity (1.48 +/- 0.08 versus 1.50 +/- 0.12) were not significantly different between the groups. CONCLUSIONS: Both lens designs showed satisfactory functional results with advantages for the diffractive lens design.     

Problems in timing of respiration with the nasal thermistor technique

Twelve normal control phakic eyes together with a number of other pseudophakic groups each consisting of 6 eyes were enrolled in this study of spatial and quantitative measurement of glare disabilities in the static visual field (Perimetric Glare Test) using an OCTOPUS 500E automated perimeter with an attached glare source. These groups were a 6 mm no hole lens group, a 6 mm 4 hole lens group, a 5.5 x 6.5 mm 2 hole lens group, a 5.0 x 6.0 mm no hole lens group and a diffractive multifocal group. Glare disabilities in the visual field were minimum in the control group. The 6 mm no hole lens group and the diffractive multifocal group showed no statistical significance compared the control group. Groups with the two types of ovoid lens and the 6 mm 4 hole lens group showed a statistically higher degree and a greater extent of glare disabilities in the static visual field than the control group. Careful selection of appropriate patients to receive implants of small efficient optic IOLs, such as IOLs with positioning holes and ovoid lenses, according to the preoperative pupil size under scotopic or mesopic condition and efficient lens optic size are important in order to reduce hole and edge glare. The diffractive multifocal IOLs group showed a slightly higher degree and a greater extent of glare than the control group and the 6 mm no hole monofocal lens group but the difference was very small and statistically insignificant. Therefore the effects of diffractive microstructure on glare disabilities were considered to be slight and clinically acceptable.     

Contrast vision and contrast sensitivity after binocular implantation of multifocal or monofocal intraocular lenses

BACKGROUND: Multifocal intraocular lenses show a reduction of contrast due to the simultaneous projection of different images to the retina. In this study we examined if there is also a loss of contrast in bilateral implantation of multifocal lenses. MATERIAL AND METHODS: We examined 22 patients with bilateral AMO ARRAY multifocal intraocular lens and compared these to 20 patients with bilateral monofocal intraocular lens. We performed a monocular and binocular examination of contrast acuify by means of Regan's contrast charts and contrast sensitivity by means of B-VAT-II-SG-Video-acuity-tester. RESULTS: Monocular examination of contrast acuity showed significant superiority of the monofocal intraocular lens at the lowest contrast. Bilateral examination of contrast acuity did not show any significant difference. Monocular contrast sensitivity of the monofocal intraocular lens was significantly superior to the multifocal intraocular lens at two spatial frequencies, but under the bilateral condition there was only a significant difference between the two lenses at the highest spatial frequency. CONCLUSIONS: Bilateral implantation of multifocal intraocular lenses enables contrast acuity and contrast sensitivity that comes very close to the performance of the monofocal intraocular lenses.     

Diffractive bifocal lens designs

Modifying the number, width, depth, and shape of the echelettes in a diffractive bifocal lens will influence the image intensity and quality within the zero, first, and higher order images. By appropriately varying these parameters optimal bifocal lens designs may be achieved.     

Theoretical and practical performance of a concentric bifocal intraocular implant lens

Some results from a survey of 43 patients who had a monofocal intra-ocular-lens (IOL) in one eye and a concentric bifocal intra-ocular-lens in the fellow eye are reported. Twenty patients with 6/9 or better post-operative visual acuity in both eyes, participated in the main part of the study. Optical transfer functions for the bifocal lens showed that, compared to an optimal single-vision correction, there is a 50% contrast degradation of the distance retinal image across all spatial frequencies above around 3 c/deg. For the patients in the main study, there was a close correspondence between practical measurement of contrast sensitivity and the theoretical predictions of the modulation transfer functions. Measuring contrast sensitivity proved an effective means of assessing misalignment of the bifocal IOLs.     

Visual results of progressive multifocal posterior chamber intraocular lens implantation

PURPOSE: To evaluate corrected and uncorrected near, intermediate, and distance visual acuities in eyes with a progressive multifocal intraocular lens (IOL) and to determine the effect of the lens on contrast sensitivity. SETTING: Multicenter study. METHODS: This prospective study comprised 59 eyes that had uneventful cataract surgery and implantation of a progressive multifocal IOL at three study centers. Uncorrected and corrected near, intermediate, and distance visual acuities were measured, as was contrast sensitivity at different frequencies. One year results are reported. Patient satisfaction was assessed using a subjective questionnaire. RESULTS: Distance visual acuity improved from 0.13 Snellen lines uncorrected and 0.23 with best correction preoperatively to 0.77 and 0.96 lines, respectively, postoperatively. Uncorrected preoperative near acuity was 13.28 Jaeger lines and best corrected acuity, 8.93 lines. These improved to 4.75 and 2.69 lines, respectively. The differences between visual acuity at intermediate distances and best distance and near acuities were not significant. Patient satisfaction was highest with vision under good light conditions and when viewing larger objects. CONCLUSION: Visual performance with the multifocal progressive IOL was adequate at various distances without additional correction. It was less satisfactory under poor light conditions.     

Influence of myopia and aging on the optimal spherical aberration of soft contact lenses

Soft contact lenses with different levels of third-order spherical aberration were tested in two samples of subjects aged between 20 and 45 years: 18 emmetropes and 19 myopes. Contrast sensitivity was measured at 12 cycles/degree to determine the optimal lens spherical aberration required by each individual. The optimal third-order coefficient was found to be negative on average in both refractive error groups. Myopic subjects required contact lenses with more negative spherical aberration than did emmetropes. The optimal aberration was also found to become increasingly negative with aging. The rate of this age-related change was faster in the myopic group. In comparison with aberration-free soft contact lenses, an improvement in contrast detection threshold of more than 25% was observed with optimal spherical aberration in half of the myopic subjects.     

A microplate fluorimetric assay for transfection of the beta-galactosidase reporter gene

Despite having been first marketed in the 1950s, new designs of progressive addition spectacle lens continue to appear. Some of the recent patent literature is reviewed on the design of such lenses. As well as a number of improvements to general purpose designs, specifically to include aspheric surfaces for the distance portion of progressive lenses, the literature includes a recent patent on an improved version of the Alvarez lateral translation lens system. The optimisation of single vision lens forms in order to extend the depth of field for early presbyopes is also discussed.     

Spectral transmittance of UV-absorbing soft and rigid gas permeable contact lenses

Increasing evidence of acute and chronic ocular effects of ultraviolet (UV) radiation has prompted some manufacturers to develop UV-absorbing rigid and soft contact lens materials. Currently, eight different lenses containing UV-absorbing agents are available in Canada. The spectral transmittance of a sample of these UV-absorbing contact lenses was measured in order to determine if all of them provide adequate protection from wavelengths in the UV spectrum. The sample consisted of 1 lens of each type. Cibasoft Ultrabloc; Permaflex UV; Boston RXD and Equalens; Alberta S; FluoroPerm 30, 60, and 92. A Philips single beam spectrophotometer was used. The lens under test was placed in a silica wet cell filled with unpreserved saline. Spectral transmittance was measured at 0.8-nm intervals over the waveband 200 to 800 nm. The results were recorded by a microcomputer interfaced to the spectrophotometer. The repeatability of spectral transmittance measurements of contact lenses using this method varied between 0% and +/- 1.55% of transmission depending on lens material and wavelength studied. The results showed that none of the rigid gas permeable (RGP) lenses, except the Alberta S, transmitted more than 0.1% (the sensitivity limit of the spectrophotometer) up to 380 nm. The Alberta S exhibited transmittance windows in the UV spectrum with peaks at 270 nm (23%) and 318 nm (29%). The Cibasoft Ultrabloc transmitted less than 1% up to 344 nm, whereas the Permaflex UV had a transmittance window in the waveband 240 to 316 nm with a maximum of 17% at 270 nm.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of the length of wear of contact lenses on corneal sensitivity

Corneal touch thresholds (CTT) were determined once in the morning before inserting contact lenses then after 4, 8 and 12 h of continuous wear. Two groups of subjects participated in this study; 12 persons wearing hard contact lenses and 15 wearing soft contact lenses. All subjects were perfectly adapted to their contact lenses and had worn them for not less than three months. It was found that hard contact lenses caused a progressive diminution of corneal sensitivity. After 12 h corneal sensitivity was, on average, 110% lower (that is an increase of the threshold) than in the morning. Soft lenses also caused a progressive reduction of corneal sensitivity which after 12 h wear was, on average, 45% lower than in the morning, although there were marked differences. Moreover, 9 of the hard contact lens subjects had been tested a year earlier and it was found that their CTT after 8 h wear had slightly but not significantly diminished which indicated that these subjects had not adapted significantly to their lenses in one year.     

Evidence for genetic linkage between the ure and trh genes in Vibrio parahaemolyticus

BACKGROUND: Many factors have been demonstrated to influence flexure of rigid contact lenses, but the contributions of surface tension and eyelid forces to flexure are not well understood. METHODS: We placed lenses on a model eye consisting of a polymethyl methacrylate (PMMA) base which could be flexed, and measured resultant flexure with a videokeratoscope. We varied the base toricity, sequence of measurement, and lens base curve. The effects of evaporation of the postlens fluid were also observed. RESULTS: Clinically significant flexure (> 0.50 D) occurred when two conditions were met: (1) the volume of the postlens space would increase if the lens unflexed, and (2) there was a paucity of fluid available to fill that space. Flexure was minimal (< or = 0.50 D) when ample fluid was present. CONCLUSION: Surface tension forces serve more to maintain rather than create rigid lens flexure. Our model helps to explain why steep-fitting lenses flex more and leads to several predictions for flexure, which appear generally to be obeyed.     

Clinical evaluation of Acuvue contact lenses with UV blocking characteristics

BACKGROUND: In response to increasing scientific evidence which indicates that ultraviolet radiation (UVR) is a potential threat to ocular health, Acuvue contact lenses (Vistakon, Johnson & Johnson Vision Products Inc., Jacksonville, Florida) have been developed which incorporate an ultraviolet (UV) blocker within the lens polymer. Data are presented for the first clinical evaluation of Acuvue lenses with UV blocking characteristics. METHOD: A double-masked, multicenter, prospective clinical trial involving 94 subjects was conducted. The study followed a randomized, parallel group design and consisted of 3 months of daily wear with two-weekly lens replacement. Two thirds of the subjects (61) wore the test lenses (Acuvue with UV blocker) and the remaining subjects (33) wore conventional Acuvue lenses (without UV blocker). RESULTS: Biomicroscopic evaluations indicated that the performance of the test and control lenses was clinically similar. No clinically relevant differences between the test and control lenses were noted in the subjective assessments of vision, comfort, or handling. In addition, no differences were shown for surface deposition, lens durability, visual acuity, and subjective symptoms. CONCLUSION: The study findings indicate that the addition of a UV blocker to Acuvue contact lenses has been achieved without affecting daily wear clinical performance. Because there is increasing evidence to suggest that the ocular tissues may be damaged by UVR, it is prudent for eye care practitioners to prescribe contact lenses that offer the benefits of both regular replacement and UV protection.     

Ophthalmoscopic assessment of the size of the optic nerve papilla

PURPOSE: To examine whether the optic disc size can be measured with common ophthalmoscopic lenses. PATIENTS AND METHODS: The horizontal and vertical disc diameters in 125 eyes of 65 patients were measured ophthalmoscopically using a commercial slit lamp with adjustable length of the beam and a Volk 60 diopters lens or a Volk Superfield lens. The refractive error of the subjects ranged between -7.25 D and +3.25 D (mean +/- S.D.: -0.34 +/- 1.77). Based on these measurements we calculated the optic disc area by applying a modified formula for an ellipse, where area = horizontal diameter x vertical diameter x pi/4. Additionally, we measured planimetrically the horizontal and vertical diameters of the optic disc on color stereo disc photographs after correcting the ocular and camera magnification according to Littmann's method. RESULTS: The values of the horizontal and vertical disc diameters evaluated on the photographs were by factors of 1.0 and 1.5 larger than those values measured with the Volk 60 D lens, and the Volk Superfield lens, respectively. Taking into account these constant linear correction factors, the optic disc diameters as measured by the Volk 60 D lens and the Volk Superfield lens varied by 0.11 +/- 0.09 mm (5.9 +/- 5.1%), and 0.11 +/- 0.09 mm (5.9 +/- 4.9%), respectively, from the values measured on the photographs. The error for the ophthalmoscopic measurement of the disc diameters decreased slightly with increasing disc size. With highly myopic eyes excluded, it was independent of the refractive error. CONCLUSION: For clinical purposes, the optic disc and other structures of the posterior fundus can be determined by ophthalmoscopy using a slit lamp and commonly used ophthalmoscopical lenses.     

What is the role of contact lenses within the scope of electronystagmography?

BACKGROUND: During electronystagmography it is necessary to correct detective vision for calibration, smooth pursuit, and saccadic eye movements. Therefore more and more people use contact lenses instead of normal glasses. Given the lack of detailed information about this phenomenon, in the current literature we decided to investigate the influence of soft contact lenses on electronystagmography. The aim of this study was to find out differences in the results of electronystagmography between using glasses or contact lenses. METHODS: Our investigation involved 20 vestibular healthy human subjects with myopia. In the first part of the examination they used their contact lenses and in the second part they were wearing normal glasses. After measuring the calibration potential we wanted to see if contact lenses would increase the rate of artifacts in the electronystagmogram. Then we attempted to determine whether contact lenses would an influence on the registration of the optokinetic nystagmus. Induced saccadic eye movements were recorded and analysed. RESULTS: Contact lenses had a negative influence neither on the calibration potential nor on the rate of artifacts. The latency of the saccadic eye movements also showed no differences between both parts of this investigation. Only the velocity of the saccades and the gain value during the optokinetic test were reduced when glasses were used. CONCLUSIONS: Contact lenses may stimulate the secretory function of the lacrimal gland and thus decrease friction forces. It is also possible that the reduced image size produced or the reduction-effect of minus by glasses in near sighted persons negatively influences eyeball velocity. In summary, our study demonstrates that contact lenses do not have a negative influence on electronystagmography. Therefore electronystagmographic studies of patients with contact lenses are permissible for purposes of documenting a medical opinion.     

Disposable contact lenses and their complications

Disposable soft contact lenses (DSCLs) have been marketed as a safer alternative to conventional soft lenses. Extended-wear DSCLs are designed for one or two weeks of continuous use before disposal. Those for daily wear are designed for use as conventional daily wear soft lenses, with daily removal and storage for 2 to 4 weeks before disposal. Beside minor complications, such as corneal abrasion, giant papillary conjunctivitis and toxic epithelial reactions to contact lens solutions, the most serious complication occurring in contact lens users is ulcerative keratitis. Several case-control studies performed over the last years, demonstrated that disposable contact lenses were associated with a 14-fold excess risk of ulcerative keratitis compared with that for patients wearing conventional daily-wear soft contact lenses and a 13-fold excess risk compared with that for wearers of rigid gas permeable contact lenses. However, the major risk factor for corneal ulceration in contact lens wearers is overnight lens wear of 1 to 3 nights. It was estimated that 49 to 74% of cases of contact lens associated ulcerative keratitis could be prevented by eliminating overnight wear.     

Anatomically accurate, finite model eye for optical modeling

There is a need for a schematic eye that models vision accurately under various conditions such as refractive surgical procedures, contact lens and spectacle wear, and near vision. Here we propose a new model eye close to anatomical, biometric, and optical realities. This is a finite model with four aspheric refracting surfaces and a gradient-index lens. It has an equivalent power of 60.35 D and an axial length of 23.95 mm. The new model eye provides spherical aberration values within the limits of empirical results and predicts chromatic aberration for wavelengths between 380 and 750 nm. It provides a model for calculating optical transfer functions and predicting optical performance of the eye.     

Accelerated study on lysozyme deposition on poly(HEMA) contact lenses

A technique was developed to accelerate lysozyme deposition on poly(HEMA) contact lenses and measure the amounts of the deposited lysozyme. This technique was for evaluation of bendazac lysine solution, a contact lens cleaning and wetting solution. Effect of temperature on lysozyme deposition on poly(HEMA) contact lenses was examined. Five temperatures ranging from 25 degrees C to 90 degrees C were chosen to examine the temperature effect. The amounts of lysozyme deposited on poly(HEMA) contact lenses at 25 C and 60 C were 0.27 microg/lens and 0.61 microg/lens, respectively. The amount increased sharply to 23 microg/lens at 70 degrees C with the maximum of 31 microg/lens at 90 degrees C. Kinetics of lysozyme deposition on poly(HEMA) contact lenses was examined at 80 degrees C. Lysozyme deposition increased sharply during the first 2 h and reached a plateau after 2 h. Effectiveness of various cleaning procedures was examined using bendazac lysine solution. When the contact lenses were washed without rubbing with fingers, the bendazac lysine reduced the amount of deposited lysozyme by more than 40% from 18.3 microg/lens to 10.6 microg/lens. The effect of bendazac lysine was most prominent when the contact lenses were shaken during storage in the presence of lysozyme in solution. If the contact lenses were cleaned by rubbing with fingers, the effect of bendazac lysine solution on the prevention of lysozyme deposition was negligible.     

Measuring oxygen tension in the anterior chamber of rabbits

PURPOSE: Measuring the concentration of oxygen in the aqueous humor without penetrating the eye would provide a new dimension in understanding aqueous humor and corneal dynamics. In this study a preinvasive method was developed for determining the cameral oxygen concentration in anesthetized rabbits by measuring the excited-state lifetime of a phosphorescent dye. METHODS: A scanning ocular fluorometer was designed to excite phosphorescence with a brief flash of light and to measure the decay of luminescence for as long as 1000 microsec after excitation. The measurement window was scanned through the depth of the anterior chamber or fixed at the mid-anterior chamber. A depot of the phosphorescent dye Pd-uroporphyrin was injected into the vitreous of eight pigmented rabbits, and within a few days the dye was measurable in the anterior chamber. The excited-state lifetime of this dye is inversely correlated to oxygen concentration and was calibrated by measuring the lifetime of dye in cuvettes equilibrated with oxygen-nitrogen mixtures. Oxygen tensions were determined from lifetimes measured in the open eye, under a polymethylmethacrylate (PMMA) contact lens, under two oxygen-permeable contact lenses, and immediately after lid closure. RESULTS: Oxygen tension in the mid-anterior chamber before placing a PMMA contact lens was 23 +/- 3 mm Hg (mean +/- SD; n = 6). After 20 minutes of PMMA lens wear, oxygen tension decreased to 4 +/- 2 mm Hg. When the focal diamond was scanned through the anterior chamber, oxygen tension was 24 +/- 5 mm Hg near the corneal endothelium and decreased to 17 +/- 8 mm Hg near the crystalline lens. Under the PMMA contact lens this gradient reversed: Oxygen tensions near the endothelium and lens were 3 +/- 2 mm Hg and 6 +/- 2 mm Hg, respectively. Lid closure for 10 minutes or longer decreased the mid-anterior chamber oxygen tension from 21 +/- 2 mm Hg (n = 19 measurements from seven animals) to 10 +/- 3 mm Hg (n = 15 measurements from five animals). CONCLUSIONS: Measuring excited-state lifetime of phosphorescent dyes in the anterior chamber provides a useful method for determining oxygen concentration in vivo, without penetrating the eye. Cameral oxygen tension under PMMA contact lenses are significantly lower than in the uncovered eye. The profile of oxygen tension through the anterior chamber suggests that oxygen is supplied transcorneally to the aqueous humor.